Plant cells and explants grown in vitro find a number of uses. For instance, cultivars with desired traits (e.g., herbicide resistance) can be more easily selected in vitro than by using whole plants. Totipotent tissue culture cells are then used to regenerate whole plants with desired characteristics. Transgenic plants can be obtained by incubating plant cells or explants with appropriate vectors capable of inserting foreign DNA into the plant genome before regenerating whole plants. Plant tissue culture cells are also useful for the production of various plant secondary metabolites which have use in a variety of contexts.
Generally, methods of plant cell tissue culture have been developed for use with angiosperms, such as tobacco. Gymnosperms, however, have not been as readily amenable to cell culture and plant regeneration. Among conifers, members of the genus Taxus are of particular interest because of their production of taxol and related taxanes. Taxane compounds, in particular taxol, have significant antitumor activity and have been the focus of investigations to develop these compounds as drugs for the treatment of cancer. These compounds have also been shown to inhibit congenital polycystic kidney disease (Woo et al. Nature 368 759 (1994)). Taxol, originally isolated from the bark of the Pacific yew, Taxus brevifolia, was recently approved by the Food and Drug Administration for use against ovarian cancer and has also shown activity against breast, lung and other cancers.
Because of the importance of cell culture techniques in many technologies, improved methods for culturing plant cells to increase, for example, the rate of cell doubling, are particularly desirable. The present invention addresses these and other needs.